Cataract surgery has greatly improved in over the past 40 years. In the early cataract surgeries, the primary method for the removal of the cataract was by intracapsular cataract extraction. This method involves the removal of the entire lens structure including the capsular bag. While this method, in conjunction with the use of special glasses or contacts, was typically effective in restoring vision, removal of the capsular bag allowed the vitreous body to move forward into the anterior area of the eye. This movement of the vitreous body can lead to postoperative complications such as retinal detachment, glaucoma, corneal decompensation and uveitis.
The introduction of microscopes to cataract surgery has allowed surgeons to improve their techniques. It is now standard to remove the nucleus and cortical material through a small incision in the anterior capsule while leaving the posterior capsule in place. This technique is referred to as extracapsular cataract surgery. Because the posterior capsule is left intact, it can help to support the vitreous body and prevent it from moving forward into the anterior portion of the eye.
Extracapsular cataract surgery significantly reduces intraoperative as well as post operative complications of cataract surgery compared to rates seen with intracapsular cataract extraction. However, complications including posterior capsule tear, zonular dialysis and intraocular lens (IOL) subluxation, can occur. In the presence of a posterior capsule tear, nuclear material and posterior chamber IOLs may subluxate intraoperatively or postoperatively into the vitreous body which may lead to many of the same complications associated with intracapsular cataract surgery. Removal of the nuclear material from the vitreous may be difficult and it involves an additional procedure called a vitrectomy. Even if all the nuclear material is removed by the vitrectomy, there is an increased risk of retinal complications.
In addition to the possibility of a posterior capsule tear, there is a risk of intraoperative traumatic zonular dialysis. The zonule fibers provide support for the lens capsule. Compromise of the zonule fibers during surgery may allow the lens capsule to subluxate into the vitreous which may lead to complications. A lens may also sublux spontaneously due to zonular dialysis from a number of metabolic and ocular conditions including trauma.
A technique to capture nuclear fragments and prevent their migration through a posterior capsule tear has been described in U.S. Pat. No. 7,186,258. A net is mechanically constrained by a device and is inserted while in the constrained configuration into the lens capsule through a small incision into the lens capsule. The net is then allowed to expand behind the nucleus. After removal of the nuclear fragments the net may be withdrawn into the device and withdrawn from the eye in the contracted configuration. This technique is not ideal because it may block removal of nuclear fragments that are between the net and the posterior capsule or nuclear fragments that have partially migrated into the vitreous body.
A technique known as posterior assisted levitation (POL) has been used to elevate nuclear fragments that have descended behind the posterior capsule because of intraoperative posterior capsule tear in order to facilitate their removal. In addition, this technique has been used to elevate subluxated lens capsules. POL generally involves insertion of a probe through the pars plana and positioning the probe behind the nuclear fragment. The tip of the probe is then elevated to bring the fragment into the anterior chamber. The probe is sometimes referred to a spatula. However, because of the small diameter of the probe, approximately 0.5-0.8 mm, balancing and elevating the nuclear fragments on the probe is technically difficult even in the hands of experienced cataract surgeons.
While the rate of complications associated with cataract surgery is low, some reports estimate the percent of complications involving the posterior capsule to be in the range of 0.5% to 5.0% and the occurrence of lens dislocation to be between 0.2% and 1.8%. Given these numbers, there is a need for additional improved techniques that can prevent complications resulting from cataract surgery.